The present application relates to semiconductor package assembly.
It is known that nano-meter size particles of a material exhibit a lower melting temperature than the material in bulk form. Thus, for the purpose of joining two bodies together it may be beneficial to use nanoparticles in order to reduce the process temperature.
WO 2004/026526 discloses a number of processes for using nanoparticles to join semiconductor parts. However, in the processes shown therein an external energy source (i.e. heat source) must be present to effect the melting of the nano-particles throughout the melting step.
It is also known to use an extremely thin stack of metals in film form to attach a semiconductor die to a heat spreader. The pre-formed films are inserted between a die and a heat spreader and react to create an alloy once an initial activation energy is applied (spark/laser or heat point).
In a process according to the present invention, the phenomenon of exothermic reaction is used as a method of efficiently joining materials together. Specifically, by using nano-sized particles of materials with exothermic properties, a low temperature initiation of the reaction can be instigated due to the particles having lower surface energy than standard micron sized particles. During the exothermic reaction, the joining layer will fully melt and then when the layer cools, a solid metallic joint with high thermal and electrical conductivity is obtained.
Exothermically reactive nano-particle paste is beneficial because it produces a metallic interface between the semiconductor die and a support body to which the die is joined with reduced thermal impedance. The method used for instigating the reaction (e.g. laser or momentary heat activation) is fast compared to the current joining processes, thus offering increased throughput at die bond/curing stage in the package assembly process.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.